Butchered cattle, bison and other dead and missing animals have been reported near Cannonball, North Dakota.
It is an area that has seen protests over the Dakota Access Pipeline.
North Dakota Stockmen's Association officials say one case involves a dead saddle horse, four dead cows, and more than 30 missing head of cattle.
The other involves three dead bison.
In both cases, some of the animals appeared to have been butchered.
The NDSA is offering a reward of up to $14,000 for information leading to an arrest and conviction.